1. Field of the Invention
This invention relates to production of alkenylbenzenes by catalytic dehydrogenation of alkylbenzenes over a potassium-based dehydrogenation catalyst. More particularly, the present invention pertains to a method for production of alkenylbenzenes which is featured primarily in the manner in which the fixed-bed of the potassium-based dehydrogenation catalyst is arranged.
The present invention, in another aspect thereof, also concerns prevention of catalyst degradation or powdering which has been difficult to avoid in a potassium-based dehydrogenation catalyst to be used for catalytic dehydrogenation of alkylbenzenes.
2. Prior art
Dehydrogenation reaction of an alkylbenzene, such as from ethylbenzene to styrene, or from p-methylethylbenzene to p-methylstyrene, etc., is industrially a very important reaction.
These reactions are carried out generally by bringing a starting alkylbenzene together with heated steam into contact with a dehydrogenation catalyst in an adiabatic system or an isothermal system reactor.
As the dehydrogenation catalyst to be used in the above reaction, potassium-based catalysts have been widely known for their excellent activity and selectivity.
As such potassium-based catalysts, K.sub.2 O-Fe.sub.2 O.sub.3 -Cr.sub.2 O.sub.3 catalysts and K.sub.2 O-Fe.sub.2 O.sub.3 -CeO.sub.2 catalysts containing K.sub.2 O-Fe.sub.2 O.sub.3 as the main component are industrially useful, and many catalysts of these systems have been proposed and are commercially available.
However, most of these catalysts, while having respective excellent features on one hand, involve problems on the other. Thus, it can be said that no catalyst which satisfies requirements as an industrial catalyst with respect to high activity, high selectivity, long life, and low cost, has yet been known.
In particular, when an alkenylbenzene is to be produced by carrying out the above reaction by the use of an industrially more practical adiabatic system reactor, it is required for reduction of its production cost to employ reaction conditions in which the amount of steam employed, that is, the steam/starting alkylbenzene (molar ratio), is lowered. In this case, if an alkenylbenzene is intended to be produced in a high yield with the use of a highly selective catalyst of the above known catalysts, the life of the catalyst becomes very short, and such a catalyst has proved to be unsatisfactory as a catalyst for industrial production in the present state of the art. In this respect, the analysis we have conducted is described in detail hereinafter.
Concerning the arrangement of the catalyst during production by catalytic dehydrogenation of an alkylbenzene, there is a disclosure in the specification of U.S. Pat. No. 3,223,743. However, it does not appear to us that the invention disclosed in this patent refers to the problem of the catalyst life.